Gypsum wallboard having a gypsum-based core reinforced on the outer major surfaces with a facing material or scrim is well-known in the art. The facing material is often paper for typically dry environments, e.g., for indoor drywall products. For some applications, however, a glass or polymer-based mat is used in products that may be exposed to high moisture conditions. For example, such board is useful in exterior sheathing products. The glass-mat gypsum board sheathing can be applied to outer studs, joists, or rafters of a home or commercial building to strengthen the structure and provide fire resistance and a degree of water resistance. The sheathing provides a base for exterior cladding (e.g., bricks, siding, stone, etc.) to be applied, with an additional moisture and vapor barrier substrate optionally applied there between.
Glass-mat gypsum board can also be utilized in indoor applications where the board may be exposed to significant moisture. For example, glass-mat faced board can be used in a variety of indoor locations, such as in sink or tub enclosures, backsplashes, etc. The glass-mat faced board provides a base for ceramic tile or the like to be applied, e.g., using mortar or mastic to secure the tile to the base. The glass mat provides a degree of water resistance and mold resistance over time in case water penetrates through the set mortar or mastic, e.g. through cracks in the tile or grout.
The manufacturing process of mat-faced gypsum board typically involves depositing cementitious slurry (e.g., a mixture containing stucco and water, where stucco refers to calcined gypsum, typically comprised primarily of calcium sulfate hemihydrate and/or calcium sulfate anhydrite) over a first mat facing material and covering the wet slurry with a second mat facing material, usually of the same type, such that the cementitious slurry is sandwiched between the two mat facing materials. The cementitious slurry is allowed to harden (e.g., forming an interlocking matrix of calcium sulfate dihydrate, referred to as set gypsum) to produce a solid article prior to final drying in a kiln.
The manufacturing process of mat-faced gypsum board, thus, often requires the facing material to be sufficiently permeable that excess water can be removed from the cementitious slurry in the drying process. For example, non-woven fiberglass mat is often used as the facing material, in which the space between the fibers provides permeability. The permeability of the fibrous mat facing material, if not treated, could reduce the water-resistance of the cementitious article because it allows water to penetrate the mat and contact the cementitious core during use. In order to alleviate this problem, exterior coatings of water resistant material are sometimes applied.
Current methods for applying the coating have been found to be inefficient. Generally, the mats are designed to be hydrophobic and repel water. A drawback is that it becomes a challenge to apply wet coatings to such hydrophobic surfaces where the wettability is poor. Because of the hydrophobic nature of the mat, during application, it becomes difficult for the wet coating to sufficiently wet or flow across the mat surface, which can lead to coating defects and defective board that can result in lost production of culled board. If a wetting aid is included to reduce the surface tension of the wet coating material, a high volume of coating is consumed by seepage through the mat, thereby resulting in significant waste.
Thus, there remains a desire for new water resistant cementitious articles, as well as methods of preparing such articles.